This invention relates to a rubber-modified thermoplastic resin which is suitable for being blended with another thermoplastic resin to impart, to the latter, an excellent mechanical strength such as tensile strength, flexural strength or the like and an excellent impact resistance and to a composition comprising the above rubber-modified thermoplastic resin and another thermoplastic resin.
Well-known rubber-modified thermoplastic resins include ABS resins and AES resins and these have been used in a large amount in industry. The following two methods for producing the ABS resin have generally been known:
(1) A method for producing an ABS resin by polymerizing 75 to 95% by weight of a monomer mixture consisting of styrene and acrylonitrile in the presence of 5 to 25% by weight of a rubbery polymer. PA0 (2) A method for producing an ABS resin by blending a high rubber content ABS resin (referred to hereinafter as the rubber-rich ABS resin) obtained by polymerizing 55 to 60% by weight of a monomer mixture consisting of styrene and acrylonitrile in the presence of 40 to 45% by weight of a rubbery polymer, with a styrene-acrylonitrile copolymer (AS resin) obtained by separately polymerizing the monomers, to adjust the rubbery polymer content in the resulting blend to 5 to 25% by weight (the ABS resin obtained by this method is referred to hereinafter as the blend type ABS resin). PA0 (1) The resin to be subjected to measurement is conditioned so that the volatile matter content under the conditions of 110.degree. C..times.60 minutes is not more than 0.1% by weight. PA0 (2) Conditions for measuring the Q value PA0 (1) Method of preparing a test piece for measuring storage elastic modulus PA0 (2) Conditions for measuring storage elastic modulus PA0 a. Rubber-modified thermoplastic resins having a rubbery polymer content of less than 50% by weight obtained by polymerizing a monomer mixture consisting of at least two types of monomers selected from the group consisting of aromatic vinyl compounds, vinyl cyanide compounds, (meth)acrylic acid esters and maleimide monomers in the presence of a rubbery polymer, in other words, rubber-modified thermoplastic resins other than the rubber-modified thermoplastic resin (A) [referred to hereinafter as the rubber-modified thermoplastic resin (C)]. Incidentally, the rubbery polymer and monomers used here may be those mentioned above. Also, the intrinsic viscosity of the methyl ethyl ketone-soluble matter of the rubber-modified thermoplastic resin is preferably 0.2 to 1 dl/g, more preferably 0.3 to 0.6 dl/g, as measured in methyl ethyl ketone at 30.degree. C. PA0 b. Copolymers obtained by polymerizing a monomer mixture consisting of at least two types of monomers selected from the group consisting of aromatic vinyl compounds, vinyl cyanide compounds, (meth)acrylic acid esters and maleimide monomers which copolymers have an intrinsic viscosity of preferably 0.2 to 1.3 dl/g, more preferably 0.3 to 1 dl/g and most preferably 0.35 to 0.7 dl/g as measured in methyl ethyl ketone at 30.degree. C. PA0 (i) Copolymers of aromatic vinyl compounds with vinyl cyanide compounds. The composition of the copolymer is preferably such that the proportion of the aromatic vinyl compound is 50 to 99% by weight and the proportion of the vinyl cyanide compound is 1 to 50% by weight. PA0 (ii) Copolymers of aromatic vinyl compounds with (meth)acrylic acid esters. PA0 (iii) Copolymers of aromatic vinyl compounds, maleimide monomers and if necessary vinyl cyanide compounds and/or (meth)acrylic acid esters.
The above method (2) can produce with a good productivity many kinds of ABS resins having different qualities by appropriately selecting the amount of the rubber-rich ABS resin blended and appropriately selecting the kind of the AS resin.
However, in the ABS industry, a further cost reduction has been required. As a measure for this cost reduction, it is considered to further increase the rubber content of the rubber-rich ABS resin and increase the amount of the AS resin blended, which AS resin is less expensive and excellent in productivity, thereby enhancing the productivity of the blend type ABS resin. However, according to the present inventors' investigation, when the rubber content of the rubber-rich ABS resin is increased as compared with conventional ones, a blend type ABS resin containing the same shows markedly such an undesirable phenomenon that fish eyes are formed, and is inferior in mechanical strength and impact resistance of molded article to the conventional blend type ABS resin using the conventional rubber-rich ABS resin.
Moreover, the rubber-rich ABS resin is sometime used in the form of a blend with other thermoplastic resins than the AS resin; and when the rubber content of the rubber-rich ABS resin is increased, the same problem as mentioned above is caused with the said blend.
The present inventors have made extensive research on a solution of the above-mentioned problems encountered by the rubber-rich ABS resin having a rubber content of 50 to 85% by weight and have consequently found that the above problems can be solved by modifying the rubber-rich ABS resin having a rubber content of 50 to 85% by weight so that the Q value of the rubber-rich ABS resin becomes 30.times.10.sup.-4 to 50.times.10.sup.-3 cc/sec. It has been further found that when the rubber-rich ABS resin is modified so that the storage elastic modulus of the acetone-insoluble matter of the rubber-rich ABS resin falls within the specific range, the above-mentioned problems can be more satisfactorily solved.